Re: [stella] "Illegal" opcodes

Subject: Re: [stella] "Illegal" opcodes
From: Ruffin Bailey <rufbo@xxxxxxxxxxxxx>
Date: Sun, 18 Jun 2000 10:08:48 -0400
> Because they aren't officially defined.  That they work at all is a side
> effect of the way the 65xx's microcode is lashed together.  Also, if you
> use a 65xx-descendant such as the 65816 (or is it the 65c816?) in the
> Nintendo Super Famicom, you will find that some or all of the 'illegal'
> opcodespace is taken up by new official opcodes which aren't compatible
> with the 65xx's unofficial ones.

Forgive my ignorance and curiousity, but who "officially" defined the
instruction set?  Are these illegal opcodes lucky by-products that just
happen to work when you use the right byte?  And then how were they

Thanks again.  It's kinda like finding out your TV has about twice the
channels you ever thought you could watch after using it without the
knowledge for about 10 years...

Ruffin Bailey

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